1. Field of the Invention
The present invention relates to a honeycomb structure.
2. Discussion of Background
In order to convert exhaust gases from automobiles, many technologies have been developed. Due partly to an increase in traffic, it is, however, hard to say that adequate measures have been taken. Further, the tendency of controlling exhaust gases from automobiles has been intensifying domestically and internationally. Particularly, NOx in diesel exhaust gas is strictly controlled. The reduction of NOx has been attempted by the control of the combustion system of an engine, but it becomes difficult for this method alone to sufficiently deal with the problem. As a diesel NOx conversion system for this problem, a NOx reduction system (called an SCR system) that reduces NOx using ammonia as a reducing agent has been proposed.
As an in-vehicle catalyst used for such a system, a honeycomb structure that contains zeolite as a catalyst component is known. In general, however, the strength of the zeolite-containing honeycomb structure is likely to be reduced. On the other hand, JP-A-61-171539 proposes a zeolite-containing honeycomb structure to which 5% through 30% by weight of inorganic fibers are added, disclosing that the zeolite-containing honeycomb structure can prevent the generation of cracks in the process of firing.
International Publication No. 2006/040874 discloses a honeycomb structure that contains ceramic particles and inorganic fibers. The inorganic fibers contained in this honeycomb structure are required to meet the condition (the aspect ratio of inorganic fibers≧(the tensile strength of fibers (GPa)/0.3)) in order to improve the bending strength of the honeycomb structure.
The contents of JP-A-61-171539 and International Publication No. 2006/040874 are incorporated by reference herein in their entirety.